Catalytic conversion system



'June 2l, 1949.

,1.12. SEI-:BOLD

CATALYTIC CONVERSION SYSTEM 3 Shee'ts-Shee'rI l Filed Jan. 30, 1943 June21, 1949. J. E. sEEBoLD 2,474,014

CATALYTIC CONVERSION SYSTEM I Filed Jan. 30, 1943 3 Sheets-Sheet 2 June21, 1949. 1 E, SEEBQLD 2,474,014

CATALYTIC CONVERSION SYSTEM w ed Deph 1155- INLET 9 v 9 I 1 Z 5 4 5 6ycles l Z 3 4 5 Cycles f'ff PKW 9501 2 4 5 Cigales i y I mr/Zey-Patented .lune 21, 1949 CATALYTIC CONVERSION SYSTEM James E. Seebold,Chicago, Ill., assignor to Stand-- ard Oil Company, Chicago, Ill., acorporation of Indiana Application January 30, 1943, Serial No. 474,120

9 Claims. (Cl. 260-.680)

This invention relates to a catalytic system and it pertains moreparticularly to temperature control in cyclic catalytic hydrocarbonconversion systems wherein a carbonaceous deposit is formed in acatalyst bed during an endothermic conversion step and is burnedtherefrom during an exothermic regeneration step in each cycle, whereinthe fluctuation in temperature of a catalyst bed of high heat capacityenables the utillzation of the heat generated during the exothermicregeneration period to supply heat required during the endothermicconversion period, and wherein there is a tendency toward thedevelopment of hot spots or cool spots in the catalyst bed as the cyclesare continuously repeated.

It is known that by admixing a substantial amount of heat retentionmaterial with the catalyst, said heat retention material being of aboutthe same particle size as the catalyst particles and uniformly dispersedthroughout the catalyst bed, the danger of overheating the catalyst inthe burning period of a single cycle can be minimized or substantiallyeliminated. The exothermic heat liberated in the burning step can beabsorbed to a considerable extent by this heat retention material andsubstantially utilized for supplying endothermic heat of reaction in thesubsequent conversion step. In this Way heat is carried from one periodto the next as sensible heat contained in the catalyst bed and isabsorbed and liberated as required by temperature uctuations in the bed.The heat retention material thus acts as a thermal ilywheel to absorbheat and liberate heat as required in this cyclic conversion system.

In most reactions of this type there will be a tendency for some pointsin the line of gas or vapor ilow through the bed to become considerablyhotter or cooler than other points in this line of iiow. The hotterpoints may get still hotter and hotter and the cool points may get stillcooler and cooler in succeeding cycles. The hotter and the coolertemperatures may get so low as to be outside the desired conversionrange while the average bed temperature is still substantially constant.An object of my invention is to minimize such temperature changes in theline of ilow through a catalyst bed, to maintain substantially all ofthe bed within desired operating temperature limits during conversion,and to avoid reaching any temperatures in the regeneration step thatmight impair catalyst activity or damage the conversion system.

A proposed method of solving this problem was to reverse the flow ofgases or vapors through the bed in alternate cycles or periodically.'I'his method can be used with some degree of success in smalllaboratory equipment and within certain rather narrow operatingtemperature ranges. In the process of converting normal lbutanes andbutenes to butadiene, fairly constant temperature can be maintained insuch laboratory equipment at a conversion level of about 1050" F., butthis is below the desired conversion level, which is at least about 1100F. for maximum butadiene production. The reverse flow idea does notsolve the temperature control problem at the desired higher temperatureconversion level because it is found that the center of the bed gets sohot as to impair the catalyst while the inlet and outlet sides of thebed get so cool as to effect no appreciable amount of conversion. Anobject of my invention is to provide a temperature control system thatlwill vbe eiective at any desired conversion temperature level.

In beds of relatively small cross-sectional area (as exempliiled bysmall scale or laboratory catalyst beds only a few inches in diameter)adequate temperature control at a relatively low temperature level maybe obtained by using reverse ow from cycle to cycle or from time to timeafter a plurality of cycles and by regulating such controllablevariables as composition of feed to the reactor, reactor pressure, spacevelocity, inlet temperature of streams, etc. However, with the beds oflarge cross-sectional area which are lrequired in commercial operationsthe regulation of temperature in one particular bed area does not insurethat temperatures in other particular bed areas will be maintainedWithin the desired operating limits. If one particular spot in thecatalyst bed gets a little too hot in one cycle of operations there is atendency -for that spot to get hotter and hotter in succeeding cycles ofoperations so that hot spots may develop at various areas throughoutthis large catalyst bed. Similarly, if a particular area gets a littletoo cool there will be a tendency for that area to get cooler and coolerwith succeeding cycles so that such area will soin be below the desiredoperating temperature range. An object of my invention is to avoid thedevelopment of hot spots and cool spots in catalyst beds of largecross-sectional area which are thus employed in cyclic conversionsystems of alternate endothermic conversion and exothermic regeneration.

I will describe my invention as it is applied to the known'laboratoryprocess of producingbutadiene from normal butanes and butenes by means 3of a mass or bed of dehydrogenation catalyst such, for example, aschromium oxide on alumina. in the presence of suflicient heat retentionmaterial such as Alundum or fused alumina so that the exothermic heatresulting from catalyst regeneration is stored in the catalyst bed andused to supply endothermic heat for the butane-butene dehydrogenation.For maximum butadiene production the conversion may be effected under arela- I tively high vacuum of about 25 inches of mercury (absolutepressure of 1 to 4 pounds per square inch) with a space velocity inthe'general vicinity of 200 to 800 volumes of gas (measured understandard conditions) per hour per volume of ac= tive catalyst (exclusiveof space occupied by heat retention material) and at a temperature inthe general vicinity of 1l00 F. During the on-stream or conversionperiod there will be a drop in temperature inthe catalyst bed which mayrange from about 50 to 100 F. or more. During the regeneration periodthere will be an increase in temperature and the temperature of catalystparticles in certain parts of the bed may be raised to approximately1200 F. or more. Usually 'about 2 volumes of the Alundum or other heatretention material is employed per volume of active catalyst, the heatretention material being of approximately the same size as the catalystparticles and being uniformly distributed throughout the catalyst bed.The on-stream or conversion period under such circumstances is about 5to 20 minutes, usually about to 15 minutes, and it is desirable to havea catalyst restoration period of about the same length of time. It is tobe expected that serious difficulties would occur if this processwereused on a commercial scale with beds of large cross-sectional area,that hot spots would develop at various points in the catalyst bed andthat these hot spots would not be adjusted or evened out in successivestages but, on the contrary, would become hotter and hotter renderingthe process inoperable. In spite of the countrys urgent need forbutadiene and the eiorts of outstanding chemical engineers to make thisbutadiene process commercially feasible, it was ruled out in connectionwith the countrys synthetic rubber program because of the questionof thedevelopment of localized areas of overheating and undercooling invarious parts of the bed, which would render the process inoperable on acommercial scale. An object of my invention is to provide a method andmeans for solving this problem and for making the butadiene processcommercially successful. 1

While my invention will be described in connection with the butadieneprocess hereinabove described it should be understoodl that theinvention is not limited thereto but is applicable to any cyclic, iixedbed, catalytic conversion process wherein the system is subject tooverheating and the development of hot spots. My invention isparticularly applicable to processes of catalytic cracking,reforming,aromatization, isomerization, or other catalytic hydrocarbonconversion process wherein said problem of temperature control mayarise. The invention is herein described as applied to the butadieneprocess merely by way of sectional area and for insuring substantiallyop' tirnum temperature conditions throughout the bed for a desiredconversion. A further object is to prevent the running away oftemperatures in to control the temperature (at a relatively low hot spotareas during regeneration. A further object is to provide improvedmethods and means of controlling the temperature of a catalyst bed oflarge cross-sectional area in order to keep it from deviating to anyappreciable extent from desired reaction temperatures over a long periodof time, i. e., throughout a large number of cycles.

A further object of the invention is to provide a conversion system'which will require a minimum amount of steel and other criticalmaterials. A further object is to provide a system which can be built atminimum cost and operated at minimum expense for obtainingmaximum-conversion and maximum yields of the desired products. Otherobjects will be apparent as the detailed de= scription of the inventionproceeds.

In the butadiene process (and in many other processes) heat producedduring the regeneration of the catalyst may be stored within a catalystbed both by catalyst and by Alundum particles or other heat retentionmaterial added for the purpose. A portion of this stored heat isconsumed by the dehydrogenation (orother endothermic reaction) occurringduring an ori-stream period. Heretoiore the successful operation of theprocess has been dependent upon the establishment of an equilibriumcondition in which the heat gained during regeneration was equal to theheat lost during reaction. If the heat gained during regenerationexceeded the heat lost during reaction the average temperature of thecatalyst bed tended to rise and vice versa. The relationship existingbetween the heat lost during reaction and the heat gained duringregeneration is dependent upon a large number of variables, including:(1) composition of feed to the reactor. (2) reactor pressure, (3) spacevelocity employed, (4) catalyst activity, (5) temperature of streams.Thus under otherwise constant conditions, increasing the proportion ofnormal butane (or the inclusion of propane) in the charge will increasethe heat absorbed during reaction relative to exothermicheat liberatedduring regeneration and the bed temperature will tend to fall. Coke'orcarbon (carbonaceous material) production increases with increase inreactor pressure; thus by increasing the reactor pressure, the heatreleased during 'regeneration is increased relative to the heat absorbedduring reaction, causing the bed temperature to increase with succeedingcycles.

By increasing space velocity, the general conversion. level is decreasedand the carbon yield per unit of conversion is decreased so that theheat absorbed during reaction is increased relative to the heat releasedduring regenerationf.v Cata lyst activity may be adjusted by changingits 'f composition and method of preparation. By adjustment of thetemperature of the streams entering the reactor during reaction andregeneration periods it is possible to obtain some measure of control ofthe average catalyst bed temperature. By the use of the above techniquesit is possible conversion level) of smallsized catalyst beds 'as used ina laboratory and this has been demonspots from the bed before unsafetemperatures are reached.

It might be possible to divide a catalyst bed into small sections orsegments and to control the temperature of each of these segments orsections by the controlled application of one or more of the abovevariables to each small section or segment. Such subdivision of thecatalyst bed would, however, oder numerous structural and operatingdiihculties and an object of my invention is to avoid the necessity ofsuch subdivision of the catalyst bed and the necessary separateregulation of the aforesaid major variables with respect to each suchsubdivided catalyst bed portion.

In accordance with my invention I employ in each catalyst restorationperiod or from time to time a step of "blowing the catalyst bed with ahot gas such as air or regeneration gas produced in the process. Iintroduce this hot gas at approximately the desired conversiontemperature. In the butadiene process I introduce it at a temperature inthe general vicinity of l100 F. with provision for varying thistemperature between about 900 F. and 1 200 F. as a normal operatingprocedure for establishing the average temperature of the catalyst bedas a whole. The amount of hot gas employed in this step is of anentirely different order of magnitude than amounts previously employedfor catalyst regeneration, e. g., is from about 4 to 40 times (in theexample herein described about six times) the amount heretofore believedto be sufficient for providing regeneration with a reasonable excess ofregeneration gas. An outstanding feature of my invention is theavoidance of any eiort toward temperature adjustment by blowing vhotcatalyst spots with cool gas or cool catalyst spots with hot gas. Asopposed to such practice I iinploy a gas of substantially uniformtemperature, preferably the approximate temperature at which conversionis to be eiected. If the average temperature of the bed as a whole tendsto rise, I may use a blow gas of correspondingly lower inlettemperature. If the average temperature of the bed as a whole y tends tofall, I may use a correspondingly higher inlet temperature of this blowgas. I employ an amount of such gas which is suiilcient to substantiallyblow out of the catalyst bed any incipient hot spots and any portions ofthe temperature pattern previously existing across various parts of thecatalyst bed which would otherwise lead to undesirable temperatures.This unique and remarkably effective process of .blowing out" incipienthot spots and objectionably high portions of the "temperature patternwill be described in more detail in connection with Figures 3, 4 and 5of the drawings after I have explained the operation of the system as awhole in connection with Figures 1 and 2.

My blowing step is separate and distinct from the regenerating stepheretofore known to the art. For regeneration, the amount of air isdependent in large degree on the amount of carbonaceous material to beburned. In the butadiene process with two parts Alundum to one partactive catalyst the carbon deposits amount to about .05 to 0.2 pound ofcarbonaceous material per cubic foot of total bed at the beginning of aregeneration period. About 8 to 32 cubic feet of air is suflicient toburn this amount of deposit, but since all of the oxygen isnot utilizeda reasonable excess of regeneration air is used. The maximum amount ofregeneration air heretofore proposed for this purpose (including thisreasonable excess) has been inthe general Vicinity of about 50 cubicfeet of air per cubic foot of catalyst bed. With a 'I1/ minuteregeneration period this amounts to a regeneration rate of about 6 to 7cubic feet of air per cubic foot; of catalyst bed per minute.

For my blowing step, the amount of air or hot gas is not dependent onthe amount of carbonaceous material but is dependent on the total massof catalyst plus heat retention material and the location of incipienthot spots or cool spots in the catalyst bed. To blow a temperaturepattern entirely out of a bed requires an amount of hot air or gas whichhas a heat capacity (mass multiplied by specific heat) roughly equal tothe heat capacity (mass multiplied by specific heat) oi the entirecatalyst bed. In the butadiene proc ess the specific heat of one poundof the catalyst bed (catalyst plus Alundum) is roughly equivalent to theheat capacity of one pound of hot air or iiue gas. If the bed density is100 pounds per cubic foot, then approximately 100 pounds of hot gas willbe required for a complete temperature pattern blow-out. Thus while 50cubic feet of air provides a reasonable excess for regeneration, Iemploy approximately 1300 cubic feet of air per cubic lfoot of cataylstfor a complete temperature pattern blow-out.

Complete temperature pattern blow-outs may be employed after .aplurality of intervening cycles. e. g., 6 cycles7 when reversed flow isemployed from cycle to cycle, but I prefer to use the hot blow step ineach cycle in a unidirectional iow system, i. e., in a system where bothcharge and air enter the same side 0f the bed at all times. Inunidirectional ow, the hottest part of the catalyst .bed is adjacent theexit side thereof and the incipient hot spots or dangerously highportions of the temperature ypattern may be blown out of this particularAlundum-catalyst bed with only about 200 to 350 cubic feet of hot air orue gas per cubic foot of catalyst bed in each cycle. For a 71/2 minutecycle this means that the blow rate should be about 25 to 50 cubic feetof hot gas per minute Der cubic foot of catalyst bed. From these iiguressimple calculations i will show that the amount of blow gas correspondsto labout'. 10% to 25% of the heat capacity of the bed. In other words,roughly about 1/5 of the temperature pattern is blown out of the bed ineach cycle. In processes such as catalytic cracking it may be necessaryor desirable to blow out more of the temperature pattern in each cycle,i. e., to employ even greater blow rates.

The regeneration air may have a small effect in displacing thetemperature pattern in a catalyst bed, but its effect for such purposeis negligible. Likewise some regeneration or combustion may' take placein my blowing operation. The regeneration step, however, produces hotspots and in repeated cycles makes them get hotter 4and hotter. Myblowing step removes hot l spots and on repeated cycles insures that allparts of the bed will be brought to or maintained withblowing step of myinvention unless a sufficient' amount of the hot air or ue gas isemployed for blowing out incipient hotspots and undesirably high or lowportions of temperature patterns across the bed.

The invention will be more clearly understood from the followingdetailed description read in conjunction with the accompanying drawingswhich form a part of this specification and in which:

Figure 1 is a diagrammatic flow sheet of a commercial butadiene plantemploying a' 4-reactor system and the use of hot air for blowing outincipient hot spots and at least a portion of the temperature patternacross the catalyst bed;

Figure 2 is a diagrammatic flow sheet of a commercial plant employing a6reactor system and utilizing hot regeneration gas as well as blow gasfor blowing out the temperature pattern across certain of the catalystbeds; v

Figure 3 is a series of graphs illustrating how the temperature patternin a vertical line through a. horizontal catalyst bed changes from cycleto cycle with unidirectional flow in the absence of my added hot gasblowing step;

Figure 4 is .a series of graphs illustrating how the temperature patterntaken in vertical line through a horizontal catalyst bed changes fromcycle to cycle with reverse ilow;

Figure 5 is a series ofygraphs illustrating in stages the effect of myhot gas blowing step in blowing out cf a catalyst bed a temperaturepattern resulting from a'series of reverse flow operations;

Figure 6 is a series of graphs illustrating the effect of my hot gasblowing step in partially blowing out of a catalyst bed the highestportion of the temperature pattern in each cycle of a unidirectionalflow-operation;

Figure 7 is an idealized chart illustrating the general type voftemperature curves that might be expected by continuously recordedtemperatures at the inlet, mid-point, and outlet of a catalyst bedemploying unidirectional ow but no blowing step;

Figure 8 is a chart as in Figure '7 where the entire temperature patternis blown out in each cycle and Figure 9 is a chart as in Figure 'l whereonly about Ve of the temperature pattern is blown out in each cycle.

The charging stock for the butadiene plant may be normal butane, normalbutenes or mixtures of normal butanes and normal butenes. The chargingstock may, of course, be obtained from natural gas or from thereductionof carbon monoxide with hydrogen (the so-called Fischer synthesis) orfrom any other natural or synthetic source. e In the example hereindescribed I employ the so-called butanes-butylenes or B-B stream ofrenery gases including butanes and butylenes from various thermal andcatalytic processes as well as from crude oil distillation. Such B-Bstream may be introduced from source I0 to feed preparation unit II.

In the feed preparation unit the charge may be prefractionated to removeany Cs or lighter hydrocarbons together with a substantial amount o! the-isobutane from the heavier normal butanebutene fraction. This heavierfraction may then be subjected to a cold acid' polymerization treatmentby treating it at about F. with 65% sulfuric acid in a conventionalrecycling system. In this treatment the isobutylene is selectivelyremoved. The unpolymerized gases are again fractionated to remove anypentanes and to remove the bulk of the remaining isobutane. The

remaining mixture of normal butanes and normal butylenes isy then passedfrom plant II by line I2 to pipe still I3. Any C'. streams which aresubstantially free from branched-chain hydrocarbons may be introduced tothe pipe vstill from line I4. Recycled butanes and butylenes areintroduced into the pipe still from line :I5. While cold acidpolymerization has been described as a preferred method of removingisobutylene it should be understood that the isobutylene may be removedby polymerization with boron uoride, aluminum chloride or other knowncatalyst at sufficiently low temperatures and under such conditions asto selectively remove the isobutylene. Any other known method ofobtaining the normal butane-normal butylene stream -may be employed andsince no invention is claimed in this particular step per se it will notbe described in further detail.

The charging stock is passed by separate pumps through separate tubes(convection tubes, wall tubes, and roof tubes respectively) I6 and I'Iin pipe still I3 and therein heated to a temperature of about 1000 to1200 F.. e. g. about 1125 F. The hot streams are then introduced throughrespective transfer lines I8 and I9 to the reactors which are on stream.Reactor A or Bis supplied via branch line 20a. or 20h from transfer lineI9 and reactor B or C is supplied via branch line 20h or 20c fromtransfer line I8. It should be understood that more than one furnace maybe employed in this system, i. e., one furnace may heat the charge toreactors A and B while another heats the charge to reactors C and D.

The reactors in the particular example herein described are cylindricalvessels about 16 feet in diameter by about 45 feet in length, lined withfused Alumina molded bricks. Across the middle of these reactors Iprovide a horizontal catalyst bed 2| about 3 feet' in depth, this bedbeing supported by a grid and structural elements (not shown) which willretain their necessary structural strength when subjected to the maximumtemperatures encountered in the catalyst regeneration. Metal parts inthe reactor which are subjected to alternate oxidizing and reducingconditions should be of high chrome (e. g. 27%) or chrome-nickel25%-20%) or equivalent material. Formation of iron oxide must be avoidedin this part of the'system. .The supporting grid must of course permitthe free flow of gases and `vapors to and from the catalyst bed. Toinsure proper distribution of vapors in the bed, this catalyst bed maybe subdivided by longitudinal and transverse vertical plates (not shown)into a plurality of individual sections and the gas flow through thesesections may be controlled by suitable dampers (not shown) operated fromthe outside of the reactor by any means known to the art.- Such asubdivision of the catalyst bed is usually not required in the practiceof my invention although it may be desirable to employ baiiles,distributors or dampers for directing the ow of charging stock and hotgases to various parts of the bed so that each part of the bed willfunction with maximum effectiveness. When upow is employed through thecatalyst bed it may be necessary or desirable to employ a retaining gridat the top as well as at the bottom of this bed or to weight the top ofthe catalyst bed to insure that the catalyst will not be blown out ofposition.

It is not essential of course that the reactor be of the size and shapehereinabove described or that the reactor drum or catalyst bed behorizontally mounted. If the drum is vertically mounted it may beprovided with a plurality of horizontal beds of approximately 3 feet indepth and the inlet, outlet and distributor conduits may be so arrangedas to maintain the ow of hydrocarbons and hot gases respectively throughsaid beds in parallel or series or series-parallel ilow. My invention isnot limited to any particular reactor structure or arrangement and itshould therefore, be unnecessary to describe alternative reactor designsin any further detail. The term bed depth as used herein is herebydefined as the dimension of the bed in the direction of charging stockor blow gas iiow. Catalyst beds 2i are of large cross-sectional area,the area of each bed in this case being upwards of about 500 squarefeet. A series of thermocouples may be placed at spaced points from topto bottom of this bed at various locations therein as illustrated bythermocouples 22, 23, and 24. By means of these thermocouples it ispossibleto ascertain the temperature pattern across the bed at anyinstant in the particular area Where the thermocouples are mounted.

The catalyst employed for the butadiene process is preferably a chromiumoxide on active alumina. Such catalysts may be prepared in the samemanner as dehydrogenation catalysts employed for other purposes andsince the preparation of such catalysts is well known to those skilledin the art the catalyst preparation requires no detailed description. Itshould be pointed out, however, that other Vith group metal oxides maybe employed instead of chromium oxide and that any other dehydrogenationcatalyst of similar properties may be employed. The catalyst material ispreferably in pelleted or granular form having a particle size of about2 to 10 mesh although larger or smaller particles may be used.

Uniformly admixed with the catalyst particles I employ a heat retentionmaterial such as fused alumina or Alundum or any other material whichhas no deleterious effect on the desired conversion and which has thenecessary properties of heat capacity and heat conductivity. About twovolumes of Alundum may be employed per volume of active catalystalthough this proportion may be varied over a relatively wide range, forexample, 4from about .5:1 to about 5:1. In some cases the catalyst orcatalyst support itself may serve as sufficient heat retention material.The specific gravity of Alundum is about 2 as compared with an activecatalyst specic gravity of about 1. The catalyst bed depth is of coursethe depth (dimension in the direction of gas or vapor flow) of the mixedcatalyst and Alundum mixture and while this bed depth is preferablyabout 3 feet it should be understood that bed depths may likewise varythroughout a relatively wide range, for example, from about 1 foot orless to 6 feet or more.

Each catalyst bed is rst brought to conversion temperature by blowing itwith a hot gas until all parts of the bed are at approximately 1050 F.This hot gas may be .air from source 25 which is heated in furnace 26 byburning a gas introduced through line 27. The air is preferably heatedto a temperature of about 1050 F. either by direct combustion orindirect heating and is passed through header 28 and branch lines 29a,29,1), 29e or 29d to the desired reactor. The heating step may beeffected at approximately atmospheric pressure or about 5 pounds gaugealthough higher pressures may be employed. During the heating the gaseswhich have passed through the bed are withdrawn through line 30a, 30h,30o or 30d and are discharged through line 3 The heat energy in thesegases may be employed for any desired purpose such as driving a turbine,generating steam, preheating charging stock, etc.

When the catalyst bed has reached conversion temperature the hot gasinlets and outlets are closed and the reactor is evacuated through line3Ia, Sib, 3io or 3|d leading to line 32 which in turn leads to anejector 33 or series of ejectors or other commercial means forevacuating the system and reducing its pressure to approximately 25inches of mercury vacuum (about 1 to 4 pounds pressure absolute). Thereaction pressure should -be as low as is commercially feasible sincebutadiene production increases with decreased reaction pressure. Whensteam or other diluent gas is employed with the B-B charge the reactionpressure refers to the Vpartial pressure of the B-B component of themixture. By using a suilcient amount of steam carbon dioxide, nitrogenor other diluent gas thesystem may be operated at atmospheric pressureor even higher and the use of ejectors may be unnecessary.

During the latter part of the evacuation step a purge or reducing gasmay be introduced into the reactor through line 34 and branch lines 35a,35h, 35e or 35d. This purge or reducing gas may be hydrogen, a fuel gasor a mixture of hydrogen and light hydrocarbon gases and it may beobtained from the product absorption unit as will be hereinafterdescribed. The purge step not only displaces any free oxygen in thereactor chamber but it preconditions the catalyst in such a way :as toreduce coke deposition in the subsequent processing period; it effects acertain amount of catalyst reduction thereby avoiding undue degradationof charging stock when the reactor is placed on stream. p

When a reactor has been brought to conversion temperature, evacuated andpurged, the hot charging stock vapors are introduced through appropriateline 20a, 2Gb, 20c or 20d and passed through the catalyst bed at a spacevelocity in the general vicinity of about 200 to 800 volumes of gas(measured under standard conditions) per hour per volume of catalyst(exclusive of space occupied by heat retention material). Based on totalbed, the feed rate is about l to 4 volumes of gas per minute per volumeof catalyst bed. The space velocity will be dependent to some extent ofcourse on the nature of feed, i. e., will be lower with increasedamounts of normal butane and higher with lesser amounts of normal butanein the feed. Space velocity will depend to some extent on the activityof the particular catalyst employed. Space velocity will also depend tosome extent on conversion temperature, i. e., will be higher with highertemperatures. The conversion temperature is preferably of the order ofabout 1100 F., i. e., is 1100 F. plus or minus about F. or preferablyplus or minus not more than about 50 to 75 F.

The reaction products may be withdrawn from the reactors through line36a, 36h, 36o or 36d to manifold 31 and thence through line 38 to quenchtower 39. I! desired of course a separate quench tower may be employedfor each reactor or for each pair of reactors. The quench tower operatesat substantially the same pressure as the reactor and in this tower thetemperature of the reaction products is rapidly reduced to approximately100 to 200 F. by means of a cooled quench oil which is sprayed in theupper part of the tower at a plurality of levels through sprays ordistributors 40. A substantially constant liquid level of quench oil ismaintained just below the outlet of line 38 and quench oil is removedfrom the bottom of the absorber through line 4|. A part or all of thisoil may be recirculated by pump 43 and cooler 44 through line 45 todistributors or nozzles 40. Quench oil from an external source may beintroduced through line 48 or 48a. A quench oil accumulator drum may beemployed with each tower or a single drum may be employed for use with aplurality of towers, the hot quench oil preferably being introduceddirectly into the drum from the base of each tower and quench oil beingpumped from the drum through cooler 4'4 to distributors 40. This quenchoil may be a relatively non-volatile hydrocarbon oil such as a gas oil.Other liquids may of course be used for this purpose and when suchliquids are not chemically altered they may simply be recycled. If theliquids are chemically altered or converted, the quenching liquid may beused on a oncethrough basis or on a continuous basis with conversionproduct removal.

To avoid possible entrainment or carry-over of quenching liquid I mayemploy suitable bailles or a bed of packing material 41l in the upper.part of the quench tower. Product vapors leaving the top of the quenchtower through line 49 pass through dry 'drum 49 from which any liquidmay be withdrawnv through line 50. Gases leave dry drum 49 through line5| to compressor 52 and are then passed through cooler 53 to dry drum49a from which any condensate may be removed through line 50a. /Gasesfrom dry drum 49a pass through lines 5mi/compressor 52a and cooler 53ato dry drum 49h from which any condensate may be removed thrbugh line50h. 'Gases from dry drum 49h pass through line 5|b, compressor 52h andcooler 53h toreceiver or separator 54. The condensed liquid is withdrawnfrom this separator through line 58. Gases from this separator passthrough cooler 59 for effecting further condensation and thence toreceiver or separator 58. Gases from the top of separator 58 areintroduced through line 59 to the base of absorber 80 which ispreferably operated at a pressure of about 150 pounds per square inchwith a top temperature in the general vicinity of about 100 F. and abottom temperature in the general vicinity of aboutv140 F. The absorberoil may be a heavy naphtha, a light gas oil or other suitablehydrocarbon introduced through line 8|. Unabsorbed gases, chiey hydrogenand llight Hydrocarbons, are withdrawn from the top of the abl sorberthrough line 82 and a part of these gases is passed through line 83 toheader 34 for supplying the'purge or reducing gas for the reactorsystem.

Rich absorber oil from the base of absorber 80 is passed through -heatexchanger 84 and heater 85 and then introduced through line 98 to anintermediate point in stripper 81 which is operated at a pressure ofabout 60 pounds gauge with a bottom temperature in the general vicinityof 300 F. and a top temperature in the general vicinity of about 120 F.A suitable heater or reboilerI 89 may be employed at the base of thisstripper and steam may be introduced through line 88a. Reiiux may beintroduced at the top thereof through line 89. Condensate from receiver54 is introduced at an upper part of the stripper through line 58. Leanabsorber oil from the base of the stripper is passed by pump 10 throughexchanger 84 and cooler 1I to line 8| 92 through line 94 to an upperpart of desorber y for introduction at the upper part of absorber 80.

The product stream leaving the top of the stripper through line 12 iscooled in cooler 19 and introduced into receiver 14. Any gases whichseparate out in this receiver are returned by line 15 to dry drum 49aor49b. Liquid from separator 59 is introduced by line 18 to receiver 14.A portion of the liquid from receiver 14 is introduced by pump 11 to thetop of stripper 81 and the remainder is scrubbed with caustic in caustictreating system 18 and then washed in water wash system 19. The washedproduct then passes through heater to a low point in extractor 9|wherein it is countercurrently extracted with a selective solvent forremoving butadiene from other hydrocarbons. The extractor may beoperated at a pressure in the general vicinity of atmospheric to 3pounds gauge with a bottom temperature of approximately 35 F. and a toptemperature of approximately 25 F., the solvent in'this case being a.cuprouscupric acetate ammonia composition known to those skilled'in theart. It should be understood that any other suitable solvent or agentmay be used for this purpose providing that system and the operatingconditions thereof are suitably modified to meet the requirements ofsuch solvent. The solvent is introduced through line 82 and cooler 83 tothe top of the extractor 8|.

The unabsorbed butanes and butylenes leaving the top of the extractorpass through line 84 to scrubber 85 wherein they are countercurrentlyscrubbed with water introduced'through line 88. The scrubbing liquid(aqueous ammonia) leaving the base of the scrubber through line 81 maybe suitably treated for recovering ammonia. The scrubbed butanes andbutenes may be passed from the top of the scrubber through line 88 tofeed preparation unit via line 89 or via line I5 to the charging stockheater. In order to prevent any buildup of isobutanes'or isobutenes inthe system it is preferred to introduce at least a part of this streaminto the feed preparation unit.

The butadiene rich solvent liquid from the base of extractor 9| isintroduced by pump 90 and line- 9| to the upper part of scrubber 92which may be operated at a pressure of about 6 pounds gauge with a toptemperature of about 34 F. and a bottom temperature of about 46 F, Theoverhead from the stripper is-introduced by line 93 toa low point inextractor 8|. The butadienesolvent liquid passes from the base ofstripper tower 95 which may be operated at a pressure of about 10 poundsgauge with a bottom temperature of about F. and atop temperature o'fabout 95 F., this desorber being provided with a suitable heater orreboiler 98. A part of the butadiene removed from' the top of thedesorber is introduced through line 191 to a low point in stripper 92for maintaining a relatively high butadiene content in the base of thestripper and insuring the removal of butenes. vThe remainder of theoverhead from desorber 95 is lremoved through line 98 to scrubber 99 andscrubbed with water introduced through line |08. yAqueous am- 13 moniais removed through line I I. The scrubbed butadiene product is pumpedfrom the top of scrubber 99 through line |02 and cooler |03 to butadienestorage tank |011.

After a reactor has been on stream for approximately minutes thecharging stock stream is diverted to another reactor and for about 21/2minutes the reactor chamber may be evacuated to remove as much aspossible of the hydrocar@ bon materials therefrom. Evacuation at thisstage is not always necessary and this evacuaa tion step may be omitted.Hot air is then introduced into the system through line 29a, 29h, 29C or29d for a period of about 7l/ minutes in amounts suiilcient to eiectboth regeneration and blowing of the catalyst to remove incipient hotspots and to blow out undesirable peaks in temperature patterns atvarious lines across the catalyst bed. While about 6 to 7 cubic feet ofgas per minute per cubic foot of total catalyst bed is suicient toeffect regeneration, I employ about 25 to 50 cubic feet of gas perminute per cubic foot of catalyst bed. During the first part of this'l1/ minute period most of the catalyst deposit is removed. During this'I1/2 minute period the incipient hot spots and peaks of temperaturepatterns across various lines of the catalyst bed are eiectively blownout of the bed. Of the gas employed during this period only about 1 to 4cubic feet per minute is required for the complete combustion ofcarbonaceous deposits, and 6 to 7 cubic feet per minute was about themaximum heretofore employed for producing a reasonable excess andinsuring sufciently complete combustion. This amount of air would notblow out incipient hot spots but would result in overheating and wouldrender the process inoperable, as has been fully demonstrated. Theadditional 18 to 44 cubic feet per minute which I employ is not for thepurpose of burning deposits but is for the purpose of blowing outincipient hot spots as will be described in more detail in connectionwith Figures 4 to 8.

After the regeneration and blowing step the introduction of hot air isdiscontinued and the reactor is evacuated for 2 or 3 minutes to removeas muchas possible of the free oxygen from the catalyst chamber.Finally, the purge or reducing gas from line 3d is passed through thecatalyst bed and discharged through lines 3! a, 3Ib, 3Ic or SId and line32 at low pressure to recondition the catalyst which is now ready toonce more go on stream with hot charging stock. This series of stepsconstitute the catalyst restoration portion or" the cycle. The timesequence of the various reactors may be as shown by the legend adjacentFigure 1. If a 21/2 minute purge follows each on-stream period, theevacuation and purge following regeneration and blowing may be reducedto 5 minutes. At any instance two reactors are on stream, one reactor isundergoing regeneration and air-blow and one reactor is undergoingeither an evacuation or reduction and purging operation. The chargingsystem, hot air system and evacuation system are each in continuousoperation.

is somewhat modied to provide for a relatively long blowout period ofabout 1% hours after six cycles each of which having a 15-minutes' onstream period and 15 minutes period of regeneration and evacuating andpurging (7l/2 minute regeneration and '7l/2 minute evacuating andpurging). In this system provision is made for reversing the flow ofcharging stock in alternate cycles. The iiow of regeneration gas isunidirectional since the direction of regeneration gas flow has littleor no appreciable effect on the temperature patterns which are developedin the catalyst bed.

In Figure 2 the reactors are designated A, B, C, D, E and F and twofurnaces I3' and I3" are employed for heating the charging stock whichis introduced from line I2. Charging stock from furnace I3 may beintroduced into any one of these reactors through transfer line andbranch lines 20a, 20'b, 20c, ZIld, 20e and 20'f where downfiow isdesired or line 2I3'a, 20'b', 20'c, 20d, 20e' or 201" where upow isdesired. Charging stock may be introduced to anyone of the reactorsthrough the same branch lines from furnace I3 and the lines are soarranged that each furnace may constantly supply the charge to one ofthe reactors on stream. Products are removed from each of the reactorsthrough lines 36'a, 36'b, 36'c, 36'd, 36's and 36'! throughcorresponding quench towers 39 to the compressors. The remainder of thecycle as well as the feed preparation, recycling, etc. will be the samein this case as in connection with Figure 1 and such features willtherefore not be repeated in connection with Figure 2. It Should be0bserved that in Figure 2 the arrangement of pipes and valves is suchthat charging stock ow through the catalyst bed may be in eitherdirection or in alternate directions in succeeding cycles. Thisarrangement of pipes and valves will be clearly apparent to thoseskilled in the art from the drawing itself and a more detaileddescription of this arrangement is therefore unnecessary The hot air maybe introduced into each of the reactors from header 28 and branchedlines ZBa, 29'2), 29'c, 29d, 29e or 29'f. The temperature of this hotair may be automatically controlled immediately prior to each. reactor.The temperature of the hoi'l air entering reactor A may be controlled byan automatic regulator I 05 controlling the amount or" gas introducedthrough line 2l to air heater 255'. Since one chamber will be undergoingregeneration and two chambers will be undergoing a blowing operation andsince it is desirable to have the inlet gas to each reactor which isundergoing the blowing operation at a temperature of approximately 1100"I provide a supplemental air system comprising an air inlet Iili, blowerIt? and cold air main |08. The temperature of the gas introduced intoreactor B will thus be controlled by temperature controller its whichvregulates the amount of air introduced through branch line IIII andhydrocarbon or other combustible gas introduced through line Iii. Ifreactor C is to undergo a blowing operation the temperature of theentering gas will be controlled by controller I2 which controls theamount of air from branch line I3 and combustible gas from branch lineII. If reactor D is to undergo a blowing operation the temperature ofthe entering gases will be controlled by temperature controller H5 whichcontrols the amount 'of air introduced through branch line IIS andcombustible gas through branch line II'I. Similarly the temperature ofgases introduced into reactor E is controlled by temperature controllerIIB and the temperature of gases entering reactor F is controlled bytemperature controller I I9.

The purging operations in this cycle will be effected in the same manneras hereinabove described in connection with Figure 1, the purge gasentering through line 34 and branch lines 35'a, 35'b, 35'c, 35d, 35'eand 35'f and the evacuated gases being removed through lines 3 I a,3I'b, 3Ic, 3Id, 3I'e and 3If through main 32' to ejector 33.

In the system of Figure 2 Aeach reactor is on stream for 15 minutes,regenerated for '7l/2 minutes and evacuated and purged for 'I1/2 minutesin each of six successive cycles with upflow and downflow of chargingstock in alternate successive cycles, and then is subjected to a hotblowing operation for a period f time corresponding to three completecycles. In this example the air rate for both the blowing andregenerating steps may be of the order of about cubic feet of gas(measured at standard condition) per minute per cubic foot of catalystbed. The purpose of this blowing step and its function of blowing outincipient hot spots and peaks of temperature patterns will now bedescribed in further detail in connection with Figures 3 to 6.

In Figure 3 I have shown a series of graphs to illustrate howtemperature patterns develop across the catalyst bed with unidirectionalcharging stock flow but in the absenceof any hot gas blowing steps.Assuming for example that the catalyst bed has been blown with hot gasintroduced at 1100" F. so that all parts of the catalyst bed are at thistemperature and that thermocouples are placed in a line through this bedas indicated by points 23 in Figure 1, the temperature reading of eachthermocouple will be 1100 F. and the temperature pattern across the bedwill be straight line :cz' of graph I. When the catalyst is regeneratedafter this on-stream period, the front or inlet end of the temperaturepattern will be lowered because the heat lost during conversion in theinlet portion of the bed has exceeded the heat gained duringregeneration. Near the discharge end of the catalyst bed the4Vtemperature will be considerably higher because the h eat gained duringregeneration in this portion of the bed exceeds the heat lost duringreaction. After this regeneration step, therefore, the temperatureacross the bed in the area of points 23 will be as indicated by line 2x,22:' of graph II. After the next cycle of on-stream and regeneration thetemperature pattern across the bed this location will be 3x, 3x' andafter another on-stream and regeneration the temperature pattern acrossthe bed will be 4x, 4x' as illustrated in graphs III and IV of Figure 3.

Even if the temperatures at areas adjacent points 22 and 24 in thecatalyst bed were identical to the temperatures in area 23 it will beseen that after three or four cycles the inlet side of the bed is toocool for effecting conversion and the discharge side of the bed is sohot as to impair the catalyst and lead to cracking rather thandehydrogenation. Such unidirectional flow without my blowing step would,therefore, be inoperative even if there were no variations intemperatures at various cross-sectional areas in the bed. The catalystadjacent thermocouples 24 may be slightly hotter than the catalystadjacent thermocouples 23 after the rst regeneration step so that thetemperature pattern' across the'bed in the area o'f thermocouples 24will be as indicated in line 2y, 2y' in graph II. During the next cyclethe temperature pattern acrossvthe catalyst bed in this area will be 3y,3y and after the following cycle it will be 43;, 4g'. It can readily beseen that a hot spot rapidly develops in the area of thermocouples 24and that after two or three cycles the catalyst in this area will beruined by high temperature. A

After the first on-stream and regeneration cycle the area adJ acentthermocouples 22 in the catalyst bed may be cooler than area 23 so thatthe temperature pattern across this area will be 2z, 2z' of graph II. Insucceeding cycles the temperature pattern of this particular area wouldchange to 32, 3e and 42, 42. It will be noted that the discharge side ofthe catalyst bed will get too hot even in the cooler catalyst area andthat while the temperature difference increases from cycle to cycle inthese various bed areas the major diiliculty is the enormously hightemperatures which are reached in a relatively short time on thedischarge side of the catalyst bed.

To solve this problem of overheating the catalyst at the discharge sideof the catalyst bed it has been proposed to use reverse charging stockflow, l. e., to pass the charging stock downwardly through the bed inthe rst cycle, then upwardly through the bed on the second cycle, thendownwardly on the third, etc. It was thought that by this method ofoperation a. uniform temperature might be maintained in the bed. Testsmade in small laboratory apparatus on beds of only a few inches indiameter have shown that with this type of operation temperaturepatterns are developed across the bed as diagrammatically illustrated inFigure 4. Starting with a uniform bed temperature of mm' at about l050F. the temperature pattern after the rst regeneration will be similar totemperature pattern 2x, 2x of Figure 3. With reverse charging stock flowduring the next on-stream period and another regeneration, thistemperature pat- Y tern will be 3m, 3m as shown in graph II of Figure 4;it will be noted that both the inlet and outlet temperatures have beenconsiderably lowered and that a peak temperature 3m" is developed at anintermediate point in the bed. After another ori-stream flow andregeneration the temperature pattern is as shown at 4m, 4m in graph IIIof Figure 4. After still another onstream period and regeneration, thetemperature pattern will be as indicated by line 5m, 5m' ln graph rVofFigure 4. It will thus obe seen that at this particular temperature areasonably uniform bed temperature maybe maintained in this bed of verylimited cross-sectional area.

Using an initial bed temperature of about 1100 F. as illustrated by 1m'of graph I, it will be found that after two periods of on-stream andregeneration the temperature pattern across the bed will be 3u, 31V andthat the peak 3u" of this curve is considerably higher than the peak 3m"of curve 3m, 3m'. After another cycle of onstream and regeneration thetemperature pattern will be 4n, 41a.' having a still higher peak 4u".After still another on-stream and regeneration period, the temperaturepattern Vwill be En, 511. with a very high peak 5u. It can readily beseen that even this small scale laboratory apparatus cannot besuccessfully employed at temperatures in the vicinity of 1100 F. becauseof the hot spots that develop near the center of the catalyst bed.

' sectional area it might be possible to control such variables ascharging stock composition, space velocities, inlet temperatures,pressure, etc. to hold a substantially constant temperature at point 23in the bed; i. e., this point of the bed might be held to a temperaturepattern corresponding tom, 5m'. At areas 22 and 24 in the bed slightlyhigher or lower temperatures would inevitably develop. `If thetemperature at point 24 became slightly higher, then a hot spot woulddevelop in this area and a temperature pattern of the type illustratedby 511., 5u would result, with a peak far above safe operatingtemperatures. If the temperature at area 22 should get a little lowerthan that at area 23 then at point 22 the temperature pattern would fallbelow the desired operating range.

Thus there are two fatal objections to the reverse ow idea for solvingthe temperature control problem: (1) the bed as a whole cannot beloperated at the desired conversion level and (2) hot spots wouldinevitably develop at various points in the large cross-sectional areacatalyst bed. Hot spots do not develop in the reverse flow system asrapidly, however, as they develop in the unidirectional flow system. Itis therefore possible to operate a bed of relatively large cross-vsectional area with reverse iiow for a few cycles before dangerous hotspots are produced. After five or six cycles it is necessary todiscontinue the conversion until the bed can be brought back to a morenearly uniform temperature. In order to bring such bed to uniformtemperature I blow it with a hot gas introduced at approximately thedesired conversion temperature and I use an amount' of gas which willhave a heat capacity roughly equivalent to the heat capacity of thecatalyst bed. The amount of hot air or other hot gas will depend on theparticular catalyst bed employed because dierent catalysts andcatalyst-heat retention mixtures will have different heat capacities.Each cubic foot of catalyst bed in the example herein described weighsroughly about 100 pounds (usually about 105 pounds). I have found thatthe speciilc heat of this catalyst bed at the desired conversiontemperature is roughly equivalent to the speciilc heat of air atsubstantially the same temperature. Therefore, I employ about 1 pound ofhot air for each pound of catalyst bed in order to effect the blowingout of the temperature pattern in the bed. For complete temperaturepattern blow-out this means that for each cubic foot of catalyst bed Iemploy roughly about 1350 cubic feet of air (measured at standardconditions). Thus in the system of Figure 2 I employed a blowing periodof about 11/2 hours. After the first 15 minutes of this blowing periodthe temperature pattern through this bed will be as illustrated by lineop Sn, En" in graph II of Figure 5. It should be noted that the coolportion of the temperature pattern is not materially warmed up nor isthe hot portion of the temperature pattern materially cooled down. Themain effect of the blowing step is to simply move the temperaturepattern towardthe discharge side oi.' the bed. If the blow gas at 1100F. meets catalyst at only 1050 F., then the catalyst is warmed up by theentering hot gas but the gas is likewise cooled down by the coolcatalyst so that it tends to cool the adjacent catalyst further over inthe bed. Likewise, when 1100 F. air passes through 1200" F. catalyst theair cools the catalyst but the air itself is heated to about 1200 F. andit, therefore, tends to heat succeeding parts of the catalyst bed tothis high temperature. The net eiect of the blowing step is thus tosimply blow the temperature pattern through the bed. Graph III oi'Flgure5 illustrates the temperature pattern after the blow is substantiallycomplete.

If the temperature pattern were only blown out to the extent indicatedby curve op 5u, Bn" in graph II of Figure 5, and then charging stockwere passed from the bottom to top of the bed in the next cycle, thepeak of the curve 5u" would be carried back to amid-point in the bed byheat capacity of the charging stock stream itself. One

volume of Cri-hydrocarbons weighs about twice as much as one volume ofair and it has a specic heat at 1100 F. about three times that of air sothat 3 volumes of charge per minute would have approximately the sameeiect in displacing the temperature pattern as would 18 volumes of air.l

In the reversed flow operations it is therefore es sential that theincipient hot spots or unduly high portions of the temperature patternbe completely eliminated in each blowing step. In the system describedin connection with Figure 2, I have illustrated such reverse owoperation with substantially complete temperature pattern blow out aftereach six cycles. I prefer, however, to employ unidirectional flow and touse a blowing step in each cycle suiilcient to blow out the unduly highportion of the temperature pattern, i. e., the incipient hot spots. Withunidirectional ilow the hottest portion of the catalyst bed will alwaysbe at the discharge side thereof Y and it is thus unnecessary to worryabout hot spots at intermediate points in the catalyst bed. Furthermore,the ow ofvr charging stock itself helps to displace the temperaturepatterns in the desired direction.

If only the conventional amount of hot air were employed forregeneration after a first on-stream period in the system described inFigure 1 the resulting temperature pattern in the bed would be as shownby line 2m, 2J." in graph I of Figure 6 (or graph 1I of Figure 3). Byemploying a gas `blow rate of 25 to 50 cubic feet yper minute per cubicfoot of catalyst bed (instead of the 6 or 7 cubic feet per minute thatwould be used for regeneration) I obtain after the first regenerationcycle a temperature pattern as illustrated by line op 2m, 25u" in graphII of Figure 6. It will be noted that the temperature pattern has beenpartially blown out of the catalyst bed, that the inlet side of thecatalyst bed is at the desired conversion temperature and that the discharge side of the catalyst bed is at a lower temperature than it wasat'the beginning of the cycle. By using this hot gas blow step in eachcycle to the extent indicated (using for example a 1/6 temperaturepattern blowout in each cycle) I obtain an equilibrium temperaturepattern roughly as indicated by line opqr in graph III of Figure 6. If acatalyst bed gets too hot at a particular area, the highest temperaturewill be adjacent the dischargel side and the incipient hot spot will beblown out during each cycle.

vI1 another area of a large catalyst bed tends to rise.

. 19 without my hot rgas blowing step causes greater and greaterdivergence of temperatures and inevitable hot spots as illustrated inFigures 3 and- 4. With a partial hot blow step in each cycle ofunidirectional fiow operation any ltemperature differences areconstantly brought into line or eliminated. My system constantly' blowsout incipient hot spots and the undesirable portions of the temperaturepattern curve and it establishes and maintains an equilibrium conditionthroughout all areas of a large catalyst bed. Without the air blow stepthe system gets out of balance with Athe inevitable development ofoperative.

In Figures 3, 4, 5 and 6 I have shown various temperature patternsacross the catalyst bed immediately after regeneration steps and beforethe catalyst goes on stream in subsequent cycles. In Figure '7 I showhow a temperature at the inlet, outlet and mid-point of the bed willvary with time in a unidirectional flow cycle operation in the absenceof my hot gas blowing step. If operations are so controlled as to bringthe temperature. of the mid-point 'thermocouple to a predeterminedtemperature level at the beginning of'each cycle then the averagetemperatures indicated by the inlet thermocouple will gradually fall andthe average temperatures indicated by the outlet thermocouples willgradually In other words, Figure '7 illustrates the type of curve thatwould be drawn by continuous recorders actuated by thermocouples mountedat the outlet, mid-point and inlet of a catalyst bed in any particularline therethrough in a unidirectional ow operation without my hot gasblowing step.

With complete temperature pattern blowout during each cycle a continuousrecording of temperatures measured by said inlet, mid-point and outletthermocouples would be substantially as illustrated in Figure 8. Withunidirectional flow. however, complete temperature blowout is notnecessary or even desirable. In Figure 9 I have illustrated the type ofcontinuous recordings that would be. registered by inlet, outlet andmidpoint thermocouples in the type of operation hereinabove described inconnection with Figure 1, i. e., using an air blow suflicient todisplace approximately 1/6 of the temperature pattern in each cycle. Itwill be noted that substantially all parts of the bed are maintainedwithin the desired operating temperature range. It should be understoodthat all ofthe above curves are more or less idealized and that actualrecordings will be less regular. The curves in Figure 8 as well as inFigure 9 and in Figure 7 may cross each other and Show considerable'fluctuations not shown on these idealized figures. The generaltemperature patterns, however, will be substantially as hereinabove setforth.

I have already stated that the nature of the charging stock has anappreciable effect on the temperatures developed in the catalyst bed.Thus when using a charging stock containing about 58% normal butenes and42% normal butanes the following data were obtained in a series ofcycles using pressure of about 2 to 3 pounds absolute, a charge rate ofthe order of about 250 cubic feet per hur per cubic foot of catalyst bed(about 750 cubic feet per hour per cubic foot of active catalyst in thebed) and an inlet transfer line temperature of approximately 1050 F.:

- hot spots which would render said system in- Inlet Ail. Inlet CatMidpoint Exit Cat- Average Tem a1 st Bed Catalyst elyst Bed Catalyst Demp. Bed Temp. Temp. Bed Temp.l

F. F. F. F. "F, 1, 1, 120 1, 095 1, 135 1, 117 y 1, 1,120 1, 095 1, 1401,118 1,120 1, 126 1, 090 1,135 1, 117 1,120 1, 1, 095 1, 130 l, 1141,110 1,120 1, 000 1,135 1,116 1,110 1,115 1,090 1,140 1,115

l Based on all thermocouples throughout the bed.

When a charging stock rich-in butanes, i. e., containing about 30%normal butenes to 70% normal butane was employed at approximately th'esame pressure and charge rate with an inlet Inlet Cate- Midpoint ExitCata- Average Ilefir lyst Bed Catalyst lyst Bed Catalyst e p Temp. BedTemp. Temp. Bed Temp.

F. F. Fl 5F. F. 1, 190 1, 160 1, 090 1, 095 1, 116 1, 1, 160 1, 095 1,095 1, 118 1, 185 1, 160 1, 095 1, 100 1, 118 l, 185 1, 150 1, 090 1,105 1, 116

Where charging stocks containing a preponderance of normal butenes isemployed, it may be necessary to employ an inlet blow gas temperature aslow as 1000 or even lower 'in order to maintain the average bedtemperature at the desired level. Thus the inlet temperature of the blowgas is varied in accordance with the nature of the charging stockandoperating conditions and it serves to maintain a substantiallyconstant average bed temperature in addition to its function of blowingout incipient hot spots and unduly high portions of the temperaturepattern across the bed.

In starting up the system as described in Figure 1, it is desirable toinitially 'go on-stream at a temperature slightly lower than the naldesired operating temperature, i. e., to go onstream at about 1050 F. ifthe desired operating temperature is about 1100 F. This is becauseunduly high temperatures might otherwise bel reached near the exit sideof the catalyst bed before the desired equilibrium operations areobtained. After a few cycles at about 1050" F. the temperature maygradually be raised to 1100* F. or higher without exceeding safeoperating temperatures at any time.

As an additional safeguard for commercial operations I may provideby-pass lines 12001 |2011, I20c and |2011 around each conversionchamber. If the temperature in any conversion chamber gets too high, thecharge to that reactor may be manually or automatically by-passed bytemperature operated control means I2Ia, |2117, 121e or 12 ld (Figure 1)so that that particular reactor will undergo the periodic blowing stepsfor blowing out hot spots or incipient hot spots without having any morecarbon deposited in the bed for augmenting these hot spots. Theby-passing of a reactor does not disturb any other part of the systemand it is discontinued when the blowing steps have' brought the catalystbed back to the desired temperature. Similar by-passes may of course beemployed in the system of Figure 2.

While my invention has been described as applied to a butadiene processit should be understood that the invention is also applicable to otherhydrocarbon conversion processes such as catalytic cracking, reforming,isomerization, etc. In these other hydrocarbon conversion processes thetemperature patterns may be somewhat different than in the butadieneprocess. -The amounts of carbon deposited may be relatively greater. Therelative distribution of the carbon through the catalyst bed may be moreuniform. The heat supplied by burning the carbonaceous deposit may bemore than sufficient to effect the desired conversion. Nevertheless. byemploying my blowing step the unduly high proportions of the temperaturepattern or incipient hot spots may be periodically blow out of thecatalyst bed or partially blown out of the catalyst bed in eacn cycle ina manner which will be apparent to those skilled in the art from theabove detailed description of my invention as applied to the butadieneprocess. While my invention has been described in great detail inconnection with certain specific examples it should be understood thatmy invention is not limited to these examples or to any of the detailsor operations thereof since numerous modifications thereof andalternative methods and operating conditions will be apparent from theabove description to those skilled in the art.

I claim: l

1. In a hydrocarbon conversion process wherein a hydrocarbon chargingstockstream is heated to conversion temperature and passed in vapor formthrough a zone of small cross-sectional area to at least one on-streamreaction zone of large cross-sectional area while at least one otherreaction zone is not on-stream, wherein each of the reaction zonescontains a large hot rmass of particles of catalytically inactive heatretention material with particles of solid catalyst materialsubstantially uniformly distributed therein and said stream is passedthrough said mass under conditions for effecting endothermic conversionby heat absorbed from said mass and a consequent temperature drop insaid mass accompanied by the deposition of a combustible deposittherein, and wherein the catalystin said mass is regenerated bycombustion of said deposit with an air stream and subsequently purgedduring an interval when the zone is not on-stream, the regenerationliberating heat for absorption in said mass and causing the temperatureof the outlet r side of said mass to become higher than the temperatureof the inlet side thereof and there normally being a change in thetemperature patterns in the line of flow through the mass with portionsthereof getting hotter-and hotter as these operations are repeated fromcycle to cycle so that there is a tendency toward the development of atleast one hot spot in an intermediate portion of said mass, the improvedmethod of operation which comprises periodically blowing each massimmediately after the regeneration and before the purging thereof,employing in the blowing step a hot blow gas having an inlet temperatureof about the desired conversion temperature, introducing the blow gas atthe low temperature side of said mass, employing an amount of blow gassuch that the product of its weight multiplied by its specific heat issubstantially less than the product of the weight multiplied by specificheat of the mass of heat retention material and cata- 22 lyst in thezone undergoing the blowing step and suiilcient to remove the highestportions of temperature patterns in themass with said blow gas butinsufficient to impart a substantially uniform temperature across thebed throughout its entire mass, employing a suilicient number of zonesso that conversion, regeneration, blowing and purging may be effectedcontinuously and continuously fractionating products of the conversion.

2. In a hydrocarbon conversion'process lwherein a. hydrocarbon chargingstock stream is heated tol conversion temperature and passed in vaporform through a zone of small cross-sectional area to at least oneon-stream reaction zone of large cross-sectional area while at least oneother reaction zone is not on-stream, wherein each of the reaction zonescontains a large hot mass of particles of catalytically inactive heatretention material with particles of solid catalyst material uniformlydistributed therein and said stream is passed through said mass underconditions for effecting endothermic conversion by heat absorbed fromsaid mass and a consequent temperature drop in said mass accompanied bythe deposition of a combustible deposit therein, and wherein thecatalyst in said mass is regenerated by combustion of said deposit withan air stream and subsequently purged during an interval when the zoneis not on-stream, the regeneration liberating heat for absorption insaid mass and causing at least part of said mass to reach hightemperatures in an intermediate portion thereof which normally tend toexceed safe limits as these operations are repeated from cycle to cycle,the improved method of operation which comprises periodically blowingsaid mass after regeneration and before purging, employing in saidblowing step a hot blow gas having an inlet temperature of about thedesired conversion temperature, employing such amount of blow gas foreach six cycles of operation that the product of the weight of the blowgas multiplied by its specific heat is approximately equal to theproduct of the weight multiplied by the specic heat of the mass of heatretention material and catalyst in the zone undergoing the blowing step.employing a suflicient number of zones whereby conversion, regenerationand blowing and purging may be effected continuously and continuouslyfractionating the conversion products.

3. In' a hydrocarbon conversion process wherein a hydrocarbon chargingstock stream is preheated to conversion temperature and passed in vaporform through a Zone of small cross-sectional area to at least oneon-stream reaction zone of large cross-sectional area while at least oneother reaction zone is not on stream, wherein each of the reaction zonescontains a large hot mass of catalytically inactive heat retentionmaterial intimately admixed with solid catalyst material in portionsWithin the range of 1:5 to 5:1, wherein said preheated charging Stockstream is passed through said mass under conditions for effectingendothermic conversion by -heat absorbed from said mass, said conversionbeing accompanied by deposition of combustible carbonaceous depositswithin the mass and by drop in the temperature of said mass and whereinthe catalyst in said mass is regenerated by combustion of said depositwith an air stream and subsequently purged, the regeneration liberatingheat for absorption in said mass and causing the temperature of theoutlet side of said mass to become higher than the temperature of theinlet side thereof, there normally being a change in the temperaturepattern in the line.

of ow through said mass with portions thereof getting hotter and hotteras these operations yare repeated from cycle to cycle so there is atendency toward the development of at least one hot spot in anintermediate portion of said mass,g

deposit, passing an additional amount of said preheated air streamthrough said mass in an amount by weight of approximately but notsubstantially greater than one-sixth of the product of the weight of themass multiplied by the specic heat of the mass and divided by the specicheat of the preheated air stream Whereby the inlet side of the mass ispreheated to approximately conversion temperature and the outlet side ofthe mass is reduced to asafe tem` perature which is higher than theinlet temperature.

4. In a hydrocarbon conversion process where-A in a hydrocarbon chargingstock stream isy preheated to conversion temperature and passed in vaporform through a hot mass of catalyst and catalytically inactive heatretentionmaterial, said mass being of large cross-sectional area and theratio of catalyst to heat retention material being within the range of1:5 to 5:1, at a conversion temperature, pressure and space velocity foreirecting endothermic conversion by heat absorbed from said' massaccompanied by deposition of carbonaceous deposits which aresubsequently burned with a hot oxygen-containing gas stream passedthrough said mass in the same direction as the charging stock wherebyheat is restored in said mass' and wherein there is a tendency for atleast one hot spot to form in an intermediate portion of said mass, thepassage of gases 'and vapors through said mass tending to shift thetemperature patterns from the inlet toward the outlet side of the mass,and wherein the mass is purged of oxygen-containing gas between theregeneration and on-stream periods, the improved method of operationwhich comprises preheating said oxygen-containing gas stream to atemperature approximating the conversion temperature and blowing throughsaid mass an amount of said preheated oxygen-containing gas suflicientto effect combustion of said carbonaceous deposits and an additionalamount by weight of said preheated gas equivalent per cycle toapproximately but not substantially greater than one-sixth the weight ofthe mass times its specific heat divided by the specific heat of thepreheated oxygencontaining gas whereby the highest portions of thetemperature Vpatterns are reduced without imparting a uniformtemperature through the entire mass.

5. A method for producing butadiene which comprises preheating a normalbutane-butylene stream to a conversion temperature of about 1100endothermic conversion of at least a part ofthe stream into butadiene byheat liberatedffromthe catalyst-alundum mass while depositingcarbonaceous material in the mass, employing a, flow Irate of about 200to 800 volumes per hour of Vthe butane-butylene stream (measured atstandard conditions) per volume of catalyst in the mass, discontinuingthe ilow of the butane-butylene stream through said mass afteranon-stream period of about f-teen minutes, then blowing through said massa stream of air which has been preheated by partial combustion with fuelto a temperature approximating said conversion temperature,'blow ingsaid preheated air through said` mass for a period of approximatelyseven and one-half minutes at a rate of about 25 to 50 volumes of pre-'4 V heated air (measured standard conditions) per minute per volume ofAlundum-catalyst mass whereby the ca rbonaceous deposits are burned, theinlet side ofthe bed is raised tosubstantially conversion temperatureand the outlet side of the bed is cooled to a safe temperature which ishigher than the temperatureV of the inlet side of the bed, purging themass for a period of about seven andone-half minutes without materiallyaltering the temperature thereof, continuously repeating the cycle, andemploying at least four separate masses of Alundum-catalyst so arrangedso that two are on stream while one is being blown and one is beingpurged.

6. lIn a hydrocarbon conversion process wherein a hydrocarbon chargingstock stream' is heated to conversion temperature and passed in vaporform through a zone of small cross-sectional area to at least oneon-streamreaction zone of large crosssectional area While at least oneother reaction zone is not onfstream, wherein each of the reaction zonescontains a large hot mass of particles of catalytically inactive heatretention material with particles of solid catalyst material substan-4tially uniformly distributed therein and said degrees F., passing saidpreheated stream at a stream is passed through said mass underconditions for effecting endothermic conversion by heat adsorbed fromsaid mass and a consequent temperature drop in said mass accompanied bythe deposition of a combustible deposit therein, and wherein thecatalyst in said mass is regenerated by combustion of said deposit withan air stream during an interval when the zone is not on-stream, theregeneration liberating heat for absorption in said mass and causing thetemperature of the outlet side of said mass to become higher than the`temperature of the inlet side thereof and there normally being a changein the temperature patterns in the line of iiow through the mass withportions thereof getting hotter and hotter as these operations arerepeated from cycle to cycle so that there is a tendency toward thedevelopment of at least one hot spot in an intermediate portion of saidmass, the improved method of operation which comprises periodicallyblowing each mass immediately after the regeneration, employing in theblowing step a hot blow gas having an inlet temperature of about thedesired conversion temperature, introducing the blow gas at the lowtemperature side of said mass, employing an amount of blow gas such thatthe product of its weight multiplied by its specic heat is substantiallyless than the product of the weight multiplied by specific heat of themass of heat retention material and catalyst in the `zone undergoing theblowing step and suflicient to remove the highest portions oftemperature patterns in the mass with said blow gas but insuflcient toimparta substantially uniform temperature across 7. The method oi claim6 in which the hydro- -carbon charging stock and the air stream arepassed through the mass of particles in the same direction andadditional amounts of the air stream.

are employed as blow gas.

8. The method of claim 6 in which the hydrocarbon charging stock and theair stream are passed through the mass of particles in the samedirection in which additional amounts of the air stream Vare employed asblow gas and in which the amount of blow gas employed in each blowingstep is such that its heat capacity is in the range or about 10% to 25%of the heat capacity of said mass.

9. The method of claim 6 wherein the hydrocarbon charging stock is abutano-butylene gas, the conversion temperature is about 1100 F., the

26 .catalyst material is chromium oxide on alumina, the heat retentionmaterial is fused alumina, the.

conditions for effecting endothermic conversion include an absolutepressure of about 1 to 4 pounds per square inch, and the air streamcontains combustion products.

' JAMES E. SEEBOLD.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,221,824 Tyson Nov. 19, 1940.2,265,641 Grosskinsky Dec. 9, 1941 2,270,715 Layng Jan. 20, 19422,321,294 Hemminger June 8, 1943 2,328,234 Seguy' Aug. 31, 19432,330,767 Weity Sept. 28, 1943 2,346,750 Guyers Apr. 18, 1944 Van Hornet al. Sept. 5, 1944

